(1) Field of the Invention
The present invention relates to a valve operating structure switchable between a position for allowing a single operating device to operate one control valve, and a position for allowing the operating device to operate another control valve. More particularly, the invention relates to a valve operating structure comprising a first and a second control valves having a first and a second slide spools, respectively, which extend parallel to each other, a control lever operatively connected to a lever interlocking member for selectively operating the first and second valve, and an interlock switching mechanism for moving the lever interlocking member between a first interlocking position to engage the first slide spool, and a second interlocking position to engage the second slide spool.
(2) Description of the Prior Art
A valve operating structure as noted above is disclosed in U.S. Pat. No. 4,553,446, for example. This known structure comprises a seesaw type link pivotally supported at a position displaced from the pivotal axis of a pivotable link operatively connected to an operating device. Opposite ends of the seesaw link are operatively connected to a first slide spool of a first control valve and a second slide spool of a second control valve, respectively. A fixing element is provided for selectively engaging an interlocking member between the seesaw link and the first slide spool, and an interlocking member between the seesaw link and the second slide spool to hold the interlocking member against sliding movement. When the operating device is operated with the fixing element acting on the second spool, the seesaw link pivots about an axis of connection of the interlocking member connected to the second spool, whereby the first spool slides to switch the first control valve. When the operating device is operated with the fixing element acting on the first spool, the seesaw link pivots about an axis of connection of the interlocking member connected to the first spool, whereby the second spool slides to switch the second control valve.
In the above operating structure, the interlock switching mechanism has a complicated construction. Because of play provided for the pivotal attachments and connections of the links and interlocking members, the operating device must be operated through a long stroke for switching the control valves, compared with the stroke of the slide spools. Further, the known structure has the disadvantage of relatively low operating efficiency with the intended slide spool remaining still and only the operating device operated without effect.